A lot of people have slept with a fan on for years and have never asked what is in the sound. It is worth knowing, because it tells you what to look for when you want the sound without the draught.
The short answer: there is nothing in it. That sounds like a joke, and it is the whole description.
A fan is the same every second. No drops, no gusts, no melody, nothing that begins or ends. There is no event in it, nothing to follow and nothing to wait for.
Rain is not like that. Rain is broadband noise with texture: individual drops, density that changes, the odd gust across the window. Waves have a rhythm. Anything with a tempo has a next beat coming. For a lot of people that movement is the whole appeal. Others keep noticing it and would rather not.
Neither reaction is a fault.
This is the most useful thing on this page if white noise has ever felt harsh to you.
White noise carries equal energy at every frequency, including the very top of your hearing, which is why it reads as bright and hissy, like a radio between stations. A fan is band limited. The motor and the blades put out a lot of low and mid energy and very little of that top end, and a wall or a door takes off more again.
So the sound most people are picturing when they say "white noise" is usually closer to a fan than to actual white noise. If you have tried a white noise track and found it sharp, you very probably did not dislike noise. You disliked the top end. A fan, or pink or brown noise, is the same idea with that part taken off.
People talk about "a fan" as though it were one sound. The single biggest split is not the size of the fan, it is whether the fan pulses.
A ceiling fan is a large slow blade passing over your head. Each pass gives a small rise and fall in the sound, and any fan that is slightly out of balance adds a wobble, a tick or a faint scrape on top of it. That is a repeating event, which a steady sound does not have.
Some people like that rhythm. Others notice it and start counting. If you have never liked a ceiling fan but you like a box fan, you are not imagining it. Try a sound with no pulse in it rather than a quieter fan.
Broad, low, plenty of body, very little pulse. The default meaning of "fan sound" for most people and the steadiest of the real fans.
Airy and open, with the blade pass in it. The most divisive one, for the reason above.
A laptop or a desk fan. Higher pitched, narrower, one insistent note.
A wall and a doorway roll the top end off it and blur it. Softer and further away in a way that turning the volume down does not reproduce, because turning it down takes the low end off, not the high end.
Air conditioning, extraction, forced air heating. Steadier than any bladed fan because you are hearing moving air rather than a rotating object, though a wide duct adds a resonance of its own.
The largest version of the same thing. Enveloping and weighted toward the low end.
Almost never because of the sound. Because of the air.
A recording gives the sound and none of that, and it goes where the fan does not.
Fan noise is the easiest sound in the world to loop invisibly, because there is no memorable moment in it to hear come around a second time. Rain is full of recognisable gusts and runs of drops. A fan has none.
The catch is that a recording of a real fan is not only the fan. It also has the motor's rattle in it, a bearing tick, mains hum, the shape of the room it was recorded in, and whatever went past the window during the take. Those repeat. Once you have heard the same little tick twice, you are listening to the loop instead of the fan, and you cannot go back.
This is the argument for a fan sound that is built rather than captured: nothing gets in that was not put in.
That is where the join lives, and where an outro voice or a fade would be. It is the least tested part of any sound app and it tells you most of what you need to know.
A tick, a wobble, a scrape, a rise and fall. If you can count it, you will notice it again.
Quiet fan noise loses its low end first, so a track that felt warm and full can turn thin and hissy.
What sounds richest in the first four seconds is not always what you want left on.
Some apps announce the next track, resume a queue, or throw an advertisement in when the thing you chose finishes. Better to find that out now than then.
Fan sounds are not a treatment and nothing here is advice about a sleep problem. What can be said is about the sound:
Luten is sound for the mind, and fan noise is where the difference between built and captured is easiest to hear, because there is nowhere for a flaw to hide.
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Luten is a wellness app, not a medical device. Nothing here is advice about treating a sleep or attention problem, and how long anyone listens is their own business.
Because a fan has nothing in it. It is the same every second: no drops, no gusts, no melody, nothing that starts or stops. Rain, waves and anything with a tempo all have events in them. If you would rather not have those, a steadier sound may suit you.
No, and this is the most useful thing to know if white noise has ever felt harsh to you. White noise carries equal energy at every frequency, including the very top, which is why it reads as bright and hissy. A fan is band limited: the motor and the blades produce a lot of low and mid energy and very little of that top end, and the room takes off more again. So a fan is closer to what most people picture when they say white noise than white noise itself is. If white noise feels sharp, a fan is usually the thing you actually wanted.
Because a ceiling fan is not steady. A big slow blade passing overhead gives a regular rise and fall in the sound, and a slightly unbalanced one adds a wobble or a tick on top of that. That is a repeating event, which a steady sound does not have. Some people like the rhythm, and some notice it and start counting. A box fan, a vent or a fan heard from another room has far less of that pulse in it.
Usually because of the air rather than the sound. A real fan cools the room, blows air across the bed, and is unwelcome in winter or when someone else is in the bed. It also moves the curtains and the papers on the desk. People who have slept with a fan for years often want the sound with none of that, and a recording is also the only version available in a hotel room, on a plane or in an office.
Better than almost anything else, because there are no memorable moments in a fan to hear come around a second time. The catch is that a recording of a real fan is not only the fan. It also carries the motor's rattle, a bearing tick, mains hum, the room, and whatever passed the window while it was being recorded. Those repeat, and once you have heard one twice you are listening to the loop rather than the fan. The last ten seconds of a track is where the join lives, so it is the quickest place to check.
Fan Noise is the steady band limited hush of a fan running in another room. Laptop Fan is a fan running close by, one note with no change in it. Air Through A Vent is air moving steadily through a wide duct with the duct in it. Cabin Noise is the low enveloping hush of an aircraft cabin at altitude, and Wide Air is open air spread across the stereo field. All of them are looped so the join is not there to find, and none of them has a voice, music or an advertisement in it.
Also worth reading: rain sounds with no thunder, white noise, pink noise and brown noise, sleep sounds with no talking and sounds for waking up at 3am.
Not sure which to try first? Answer two questions and get one sound to start with.